In a cellular communications network, user equipment (UE) (such as mobile telephones, mobile devices, mobile terminals, etc.) can communicate with other user equipment and/or remote servers via base stations. LTE systems include an Evolved Universal Terrestrial Radio Access Network (E-UTRAN) and an Evolved Packet Core (EPC) network (or simply ‘core network’). The E-UTRAN includes a number of base stations (‘eNBs’) for providing both user-plane (e.g. Packet Data Convergence Protocol (PDCP), Radio Link Control (RLC), Medium Access Control (MAC) and PHYsical (PHY) layers) and control-plane (e.g. Radio Resource Control (RRC)) protocol terminations towards the UE.
In order to provide seamless connectivity for the mobile devices, the base stations are configured with a list of their neighbour base stations so that the mobile devices can be handed over to one of the cells operated by other base stations when necessary (e.g. due to mobility of the mobile devices and/or changes in signal conditions and/or load balancing, etc). Therefore, each base station is required to store information relating to its neighbours including, inter alia, identifiers of the cells operated by each (known) neighbour base station, a unique identifier (e.g. eNB Id) associated with each neighbour base station, and a respective transport network layer (TNL) address associated with each neighbour base station. The TNL address facilitates communication between base stations via a so-called X2 interface, which is provided between each neighbour base station pair. The X2 interface uses the Stream Control Transmission Protocol (SCTP) to transmit data between the base stations.
Each base station can obtain the TNL address associated with another base station by following a so-called TNL Address Discovery procedure specified in section 22.3.6 of 3GPP TS 36.300 V11.5.0, the contents of which are incorporated herein by reference. In summary, whenever a particular base station discovers a ‘candidate’ neighbour base station, it can request the so-called Mobility Management Entity (MME) in the core network to transfer configuration information between the two base stations via an S1 interface (which is provided between each base station and the core network). This procedure needs to be followed whenever there is a change in the configuration of one of the base stations and/or whenever a base station or a cell is added to (or removed from) the network to prevent handover problems for the mobile devices (e.g. incorrect selection of a handover target cell, which might result in loss of connection) in the vicinity of such cells. Since conventional (macro) base stations operate in an always-on mode and their configuration does not change often, this procedure does not cause unnecessary load on the core network elements and the S1 interface between the eNBs and the MME.
The 3GPP standards body has adopted an official architecture and defined standards for home base stations (‘HNB’). Where a home base station is operating in accordance with the LTE standards, the home base station is sometimes referred to as a HeNB. A similar architecture is also applied in the WiMAX network. In this case, the home base station is commonly referred to as a femto cell. For simplicity, the present application will use the term HeNB to refer to any such home base station and will use the term eNB generically to refer to other base stations (such as the base station for the macro cell in which a HeNB operates). The HeNB can provide radio coverage (for example, 3G/4G/WiMAX) via one or more cells within a home, small and medium enterprise environment, and/or in public places (such as shopping malls and the like). The HeNB connects to the core network via a suitable public network (for example via an ADSL link to the Internet) or operator network and in the case of the 3GPP standards, via a so called small cell gateway (e.g. including the functionality of a so called HeNB-GW) which typically aggregates traffic from several HeNBs.